P08027: Wireless Assistive Control System


Table of Contents

Visual Feedback Testing

This page serves to document the procedures taken to setup and configure lighting controls for visual feedback to the user.


The purpose of the lighting components on the vehicle are to provide information to the person controlling the vehicle as to how they are affecting the commands issued to the vehicle. The lights will serve as a visual feedback mechanism.

Persistence of Vision (POV)

Each LED bar on the vehicle is controlled through a demultiplexer, as a result only one LED can be lit at a time. The desired functionality of the LED bar is that multiple LEDs would be lit at the same time. To achieve this functionality, each LED is lit sequentially in rapid succession. This gives the appearance to the user that multiple LEDs are lit simultaneously.


The lights are configured such that they are able to communicate to the user the direction and magnitude information which is constantly being communicated to the RC vehicle.

Left and Right

A light bar placed across the back of the vehicle indicates to the user the direction in which the vehicle is being told to travel as well as the magnitude in that direction.

The LED bar across the back of the vehicle has been laid out in a manner such that the magnitude information is indicated to the user in a logical manner. This design decision results in the bit resolution to be reduced by a factor of two when turning in either direction. In other words there are only 4 discrete magnitude indication levels for either left or right motions.

add image of led board

Forward and Reverse

Similar to the left and right controls, LED bars are positioned at either side of the vehicle to indicate the magnitude of travel in either the forward or the reverse direction.

Unlike the left and right configuration, the lights for forward and reverse control have full 8-bit resolution. When the user is traveling forward the lights will be lit from the rear to the front of the vehicle (green to red). When the vehicle is traveling in reverse the LEDs will light in the opposite direction, starting at the front of the vehicle and lighting towards the back as the magnitude increases(from red to green).

add image of led board

Testing / Results

A tool which was of great use in debugging the lighting control subroutines, was Terminal.[1] This is the same application used for testing the motor controls.

A simple test application was written for Terminal's scripting feature. This script periodically instructs the vehicle to change its direction of travel. This allows for simple visual verification that the lights are illuminating in the appropriate order to correctly indicate the instructed command. A copy of the script used can be found here.

Persistence of Vision (POV)

After implementing the subroutines which control the LEDs the average rate at which the LEDs were refreshed was approximately 11kHz. This is significantly higher than the human eye is capable of perceiving.

This value can fluctuate depending on the wireless communications baud rate or the addition of instruction to the microcontrollers main loop, however the decrease in refresh rate should not reach a perceivable level unless significant changes are made to the code.


  1. Terminal - simple serial port terminal emulation program